Technical Field
The present invention relates to an anti-seismic isolator. The invention relates in particular, but not exclusively, to a seismic isolator adapted to be used to isolate storage load-bearing structures, industrial shelving units, scaffoldings and the like, with respect to the bearing pavement. The invention can also be applied in all those cases in which it is necessary to protect these structures and their contents, if any, from the consequences deriving from unwanted movements consequent for example to accidental shocks due to the loading and unloading of goods with lifting and transport means.
Description of the Related Art
Nowadays many jurisdictions have adopted regulations requiring the adoption of measures aimed at reducing damage to property and persons, resulting from a seismic event.
In the case of a shelving unit, the effect of an earthquake may not only cause the failure of the load-bearing structure, but more frequently it can affect its stability, with the consequent risk of tipping or falling objects.
This phenomenon can be particularly detrimental in the case of industrial shelving units placed, for example, in crowded sale premises, such as those in a department store.
Anti-seismic isolators are devices developed to protect structures of various types, from the effects of an earthquake.
Single or double pendulum anti-seismic isolators are known, which are generally used for large structures, such as bridges or buildings. These are anti-seismic devices which generally comprise a hemispherical structure, slidable on a sliding surface on which sliding materials are arranged, which cause the viscous damping of the vibrations.
WO2009034585 (A1) discloses an example of a pendulum anti-seismic isolator, provided with elements sliding perpendicularly with respect to other.
U.S. Pat. No. 3,146,979 discloses an anti-seismic isolator comprising a pair of parallel circular plates arranged horizontally, between which a plurality of spheres is provided. The lower plate is arranged against the ground and the upper plate serves as a support for the structure to be protected. The spheres between the plates are housed in a circular channel, the section of which is larger than the diameter of the spheres. The device allows a mutual movement between the plates when they are stressed by cross vibrations or shocks. In such conditions, the shape of the channel in which the spheres are housed causes the upward displacement of the upper plate and thus most of the horizontal component of the energy is converted into a vertical component.
WO-A-00/37823 discloses an isolating apparatus against the vibrations induced by an earthquake and comprises a pair of plates interconnected by a sliding element arranged at the center and associated with each other at the periphery by means of elastic connecting arms. The central sliding element allows mutual horizontal displacement of the plates, while the elastic arms determine the return of the plates in the initial position.
U.S. Pat. No. 3,638,377 describes an earthquake-resistant warehouse structure for the storage of material, wherein the support feet of the structure are designed so as to allow a relative displacement between the structure and the pavement.
Another example of an anti-seismic protection device is described in U.S. Pat. No. 4,330,103. Also this method provides for plates sliding horizontally relative to each other equipped with elastic elements and friction material to dampen oscillations.
An improved anti-vibration isolator is described in JP-A-4 330 103. This device is provided with a pair of horizontal parallel plates, between which sliding elements are arranged that are associated with elastic elements, which tend to bring the plates back to the starting position.
WO 2005/049942 describes an interface isolator/dissipator for interfacing between the ground and supporting structures comprising a supporting base attachable to the ground, which supports a contact base that can be associated, by way of kinematic connecting means, with a lower portion of at least one supporting upright of a supporting structure; between the contact base and the supporting base there are interposed interface means that are adapted to allow the contact base to move with respect to the supporting base at least along two directions parallel to the ground. The isolator/dissipator is also provided with return means, operating between the supporting base and the contact base, adapted to control the relative displacement between the supporting base and the contact base.
A device intended to reduce the intrinsic stiffness of a supporting structure, such as an industrial shelving unit or the like, is also described in IT-1 327 395. However, unlike the previous solution, this device does not allow the damping of vibrations along a multiplicity of directions.
The known solutions have a series of drawbacks, which can be summarized in the substantial inability in simultaneously fulfilling different needs, which are, however, crucial for the proper operation of the isolator in all conditions.
A first requirement stems from the need for the isolators to oscillate with their own frequency of oscillation, independent of the mass of the associated structure. This need is particularly evident in the case of shelving units that are subjected to loads that considerably vary over time.
Moreover, the isolator must be capable of withstanding vertical compression or traction loads directly on the isolating element.